ML20090D666

RO 50-20/92-1 on:920218,malfunction Occurred in Reactor Analog Controller Due to Improper Performance of Increase in Reactor Power.Caused by Operator Error.Analog Automatic Control Sys Investigated & Temporarily Repaired

ML20090D666
Person / Time
Site:	MIT Nuclear Research Reactor
Issue date:	03/02/1992
From:	Bernard J, Kwok K MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
50-20-92-1, NUDOCS 9203060383
Download: ML20090D666 (5)

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• NUCLEAR REACTOR LABORATORY AN INTERDEPARTMENTAL CE NT ER OF MASS ACHUSE*TS INSTITUTE OF TECHNOLOGY k.h7

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O K. HARLING 138 Albany Street, Camtitdge. Mass 02139 J A BERNARD. JR.

Director TeMax No. 10171253 7300 Deector of Reactor Operrions Telen No 92-1473 MIT CAM Tel No (617)253 4211/4202 March 2,1992

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U.S. Nuclear Rcgulator/ Commission Washington, D.C. 20555 Attn: Document Control Desk

Subject:

Reportable Occurrence 50-20/1992-1, Improper Increase of Reactor Power Causing a Brief Excessive Power Level 1 Gentlemen:

Massachusetts Institute of Technology hereby submits this ten-day report of an ocentrence at the MIT Research Reactor (MITR) in accordance with paragraph 7.13.2(d) of the Technical Specifications. An initial report was made by telephone to NRC Region I (Mr. Thomas F. Dragoun) on February 21,1992. A telephone report was also made to NRC lleadquaners, Mr. Alexander Adams, on the same day. These telephone reports were delayed beyond the normal 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> because this occurrence was not identified by the MITR's u:nior staff until late on February 20,1992. This is further discussed in the

• report.

The format and content of this report are based on Regulatory Guide 1.16, Revision 1.

1. Reoort No.: 50-20/1992-1 2a. Repon Date: 2 Man:h 1992 2b. Date of Occunencc: 18 February 1992

3. Facility: MIT Nuclear Reactor Laboratory 138 Albany Street.

Cambridge,MA T139

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Reportable Occurrence 50-20/921 Page 2

4. Idsgifcation of Oc' . xnce:

Impmper t>erformance of an inc* case in reactor power so that as a result of manual withdrawat of individual shim blades, the reactor's neutronic power att'dned 5.25 MW. The control devices were then inserted with the result that the total time for which the neutronic power exceeded 5.0 MW was about 22 s *1 his occurred at 1921 on 18 February 1992. The reactor's thermal power, which is continuously computed by a calorimetric balance and recorded, never exceeded 4.69 MW.

S. Conditions Prior to Occurrence:

The reactor was on analog automatic control at steady-state with the shim bank at 15.40 inches, The regulatin;; rod which was connected to the analog 3 controller was at 7.04 inches. Channei #7, the linear flux channel, was indicating 84.8 p.a which contsponds to 4.8 MW. TR reactor had been at this power level for about 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and had not yet attained thermal equilibrium. As a result, the thermal power was 4.69 MW. Several experiments were in propess, including one which required a near-constant temperature envimnment. This in turn meant that the power level had to be maintained constant.

6. Descriotion of Occunence:

The performance of reactor power increases at the MIT Rescamh Recctor is governed by written pmcedures that have been reviewed and approved by the MIT Reactor Safeguards Committee (MITRSC). These procedures rec uire, among other things, that (1) reactor power be increased on a period that is ..onger than 100 s whenever power is within 80% of the demanded level and (2) that two licensed operators, one of whom holds a senior license, be present in the control room during any power increase of more than 10%.

At approximately 1921 on February 18,1992, a malfunction occurred in the reactor's analog controller with the result that the regulating rod was continuously inserted until it reached its near-in limit. This caused the reactor's neutronic power,-

as indicated by channel #7, to decrease to 33.0 pa (1.87 MW). The console operator, a licensed senior operator, then took manual control of the reactor and notified the Duty Shift Supervisor and the Reactor Superintendent of the problem.

Permission was given for a return to the i mal operating power. The operator was anxious to minimize the temperature perturbation to the on-going experiment and therefore, instead of waiting for the Duty Shift Supervisor to reach the control -

room, asked another operator, who was in the immediate area, to witness the power increase. This was an acceptable practice except that the increau was imtiated before the second operator had fully reviewed the situation. The console operator sequentially raised each of the reactor's six shim blades by several tenths of an inch so as to create a positive period and to maintain a uniform bank height, This was in accordance with the governing procedure, except that enough reactivity was inserted to create a reactor period of about 50 s tnd, contrary to the approved procedure, the operator maintained this period until approaching the desired pow -

level. He then began to insen the shim blades sequentially, but was unable to negate completely the positive period because the differential reactivity worth of an

' individual blade at a height of about 16.00 inches is not sufficient to immediately_

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Reportable Occurrence 50-2092-1 Page 3 offset the reactivity associated with a 50-s period. As a result, an overshoot of the neutronic power occurred. This is shown in the attached figure which is the strip-chart reco~iing oflinear flux channel #7. (Nag: Once it was a aparent thr.t the power would overshoot, the operator drove one of the silm blades in continuously.) An error in judgment was then made in that the console operator did not notify the Reactor Supenntendent of the overshoot. As a result, the occurrence was not identified by the MITR's senior staff until the evening of February 20, 1992.

7. Description of Apparent Cause of Otcunence:

'Ihe apparent cause of this occurrence was operator error in that the operator performed a power increase on a period shorter than 100 s while tne power was within RO% of the dernanded level. L

8. Analysis of Occena:

The reactor's neutronic power, as measured by the trace recorded on the strip chart for channel #7 (the linear flux channel) cached 5.25 MW and was above 5.0 MW for 22 s. The reactor safety system is set to activate at 5.5 MW and this level was not reached. Reactor power, as recorded on the thermal power strip chart, did not exceed 4.69 MW It should be noted that the MITR-II Facility Operating License is written in terms of thermal power and hence no limiting condition for operation was exceeded.

It is not expected that an excursion to the 5.25 MW neutronic power level reached in this case, which is well below the authorized limiting safety system setting of 6 MW, would in any way cause any damage to the reactor. Nevertheless, ,

analyses were made of the primary coolant. No abnormalities were identified. The core purge gas monitor was norraal and a subsequent visual inspection of the reactor core revealed no abnormalities. These actions confirmed that no damage -

7 occurred to the n: actor.

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9. Corrective Action:

The following corrective actions have been :aken:

(a) This occurrence was reviewed verbally with the operator in question with emphasis on the proper conduct of power increases.

(b) The Senior Review Board met to discuss the occurrence and decided to require tha' the operator involved complete a special review of the procedures and principles that govern power increases. (Action to be completed by 13 March 1992.)

(c) The Senior Review Board also decided that the protocol for information exchange between operators, the details of this occurrence, and the criteria for notifying the senior MITR stat'f of occurrences be reviewed by all

. licensed operators. (Action to be completed by 30 April 1992.)

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. 4 Reportable Occurrence 50-20921 Page 4 L .

(d) Investigated and repaired analog automatic control system. (Temporary repair completed 25 February 1992 Permanent trpair is still pending.)

10. Failure Data:

An improper reshim that resulted in an overshoot of the neutronic power occurred on 19 November 1987, (See ROR #50-2Qfl987-2.)

Sinenrely,

(

Kwan S. Kwok, h6h. k Superintendent i

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John A, Best ud, Ph.D. ~

Director of Reactor Operations MIT Research Reac'or JAB:CRH

Attachment:

Figure One cc: MITRSC USNRC- Region I- Chief,' , .

Reactor Projects Se; tion No. 3A USNRC - Region I- Reactor Engineer, Reactor Projects Section Nn. 3A USNRC- Project Manager, Standardization and Non-Power Reactor lioject Directorate USNRC - Region I - Chief, . .

Effluents Radiation Protection Branch .

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Reportable Oxurrerne 5420921 Page5 i

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